Electrochemical apparatus with retractable electrode

ABSTRACT

Electrochemical apparatus and methods that support periodic, non-steady state, or discontinuous operation without suffering degradation of materials or loss of efficiency. The invention provides a means for positioning one or more electrodes into contact with electrolyte and means for retracting the one or more electrodes out of contact with the electrolyte. The means for positioning and means for retracting may be the same device or different devices. The means for positioning and means for retracting may be designed to provide automatic, passive, or fail-safe retraction of the electrode upon a given shutdown condition, such as a voltage of less than one Volt being applied between the first and second electrodes, expiration of a time period, an ozone concentration greater than a setpoint ozone concentration, contact pressure of less than 5 psig, and combinations thereof.

[0001] This nonprovisional application is a continuation-in-partapplication of U.S. nonprovisional application Ser. No. 09/598,067 filedon Jun. 20, 2000, and claims priority of U.S. provisional applicationNo. 60/254,820 filed on Dec. 12, 2000, U.S. provisional application No.60/261,101 filed on Jan. 10, 2001, U.S. provisional application No.60/261,534 filed on Jan. 12, 2001, and U.S. provisional application No.60/317,562 filed on Sep. 5, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to an electrochemical apparatus capable ofperiodic operation without suffering long-term loss of efficiency ordegradation of materials, in particular electrocatalyst layers orcoatings.

[0004] 2. Background of the Related Art

[0005] Ozone is known to be a powerful oxidizing species. Numerousmethods and apparatus have been used to generate ozone and use ozone.However, many potential applications for the use of ozone do notrequire, or cannot utilize, a continuous stream of ozone gas or ozonatedwater. Unfortunately, the generation and use of ozone in discontinuous,unsteady-state, or batch modes of operation can be problematic for avariety of reasons. First, the high reactivity and rapid decompositionof ozone necessitate that the ozone be generated just prior toutilization. This dictates that ozone-generating capacity must closelymatch the peak rate of consumption. Second, the need to generate highlyconcentrated ozone favors electrochemical processes, most preferablyusing a lead dioxide anodic electrocatalyst.

[0006] While lead dioxide (PbO₂) is generally unstable in aqueous acidsolutions, the potential-pH equilibrium diagram for lead-water at 25° C.in FIG. 1 shows that maintaining a high positive electrode potential,with respect to the standard hydrogen electrode (SHE), on the positivePbO₂ electrode in an electrochemical apparatus can stabilize leaddioxide. Therefore, lead dioxide instability in acid solutions is easilyavoided in continuous electrochemical processes since a relatively highelectrical potential is continuously maintained across the positive andnegative electrodes. Where the electrochemical process is needed onlyperiodically, it is possible to reduce the rate of the electrochemicalprocess while supplying a lower electrical potential across the positiveand negative electrodes, which stabilizes the lead dioxide bymaintaining a trickle of electrical current between the electrodes.Unfortunately, continuous electrochemical processes and continuouselectrical potentials are not practical in numerous applications, suchas residential or consumer products, since power outages and evendrained backup batteries can be experienced. Yet another possiblesolution is to use platinum metal as the anode electrocatalyst, but thepenalty for using platinum is a lower ozone yield and higher cost.

[0007] Central to the operation of any electrochemical cell is theoccurrence of oxidation and reduction reactions that produce or consumeelectrons. These reactions take place at electrode/solution interfaces,where the electrodes must be good electronic conductors. In operation, acell is connected to an external load or to an external voltage source,and electrons transfer electric charge between the anode and the cathodethrough the external circuit. To complete the electric circuit throughthe cell, an additional mechanism must exist for internal chargetransfer. Internal charge transfer is provided by one or moreelectrolytes, which support charge transfer by ionic conduction.Electrolytes must be poor electronic conductors to prevent internalshort-circuiting of the cell.

[0008] The simplest electrochemical cell consists of at least twoelectrodes and one or more electrolytes. The electrode at which theelectron producing oxidation reaction occurs is the anode. The electrodeat which an electron consuming reduction reaction occurs is called thecathode. The direction of the electron flow in the external circuit isalways from anode to cathode.

[0009] Electrochemical cells in which a chemical reaction is forced byadded AC/DC electrical energy are called electrolytic cells.Electrochemical cells also include fuel cells, which are supplied withfuel to bring about the generation of DC current, and batteries, such aszinc/manganese dioxide.

[0010] The electrolyte may be a liquid electrolyte (aqueous or organicsolvent, with a dissolved salt, acid or base) or a solid electrolyte,such as a polymer-based ion exchange membrane that can be either acation exchange membrane (such as a proton exchange membrane, PEM) or ananion exchange membrane. The membrane may also be a ceramic basedmembrane, such as ytria-stabilized zirconia which is an O⁻² ionicconductor.

[0011] However, ozone (O₃) may be produced by an electrolytic process,wherein an electric current (normally D.C.) is impressed acrosselectrodes immersed in an electrolyte. The electrolyte includes waterthat dissociates into its respective elemental species, O₂ and H₂. Undersuitable conditions, the oxygen is also evolved as the O₃ species. Theevolution of oxygen and ozone at the anode may be represented as:

2H₂O=>O₂+4H⁺+4e ⁻

3H₂O=>O₃+6H⁺+6e ⁻

[0012] Utilization of high overpotentials, such as anode potentialsgreater than 1.57 Volts, and certain electrocatalyst materials enhanceozone formation at the expense of oxygen evolution. The water oxidationreactions yield protons and electrons which are recombined at thecathode. Electrons are conducted to the cathode via the externalelectronic circuit. The protons are carried through a solid electrolyte,such as a proton exchange membrane (PEM).

[0013] The cathodic reactions may utilize hydrogen formation:

2H⁺+2e ⁻=>H₂

[0014] or involve the reduction of oxygen as follows:

O₂+4H⁺+4e ⁻=>2H₂O

O₂+2H⁺+2e ⁻=>H₂O₂

[0015] Specialized gas diffusion electrodes are required for the oxygenreduction reaction to occur efficiently. The presence of oxygen at thecathode suppresses the hydrogen formation reaction. Furthermore, theoxygen reactions are thermodynamically favored over hydrogen formation.In this manner, the reduction of oxygen to either water or hydrogenperoxide reduces the overall cell voltage below that required to evolvehydrogen.

[0016] Therefore, there is a need for an electrochemical apparatus andmethods that support periodic, non-steady state, or discontinuousoperation without suffering degradation of materials, includingelectrocatalysts, or loss of efficiency. It would be desirable if theapparatus and methods did not require operator attention to verify thestatus of the power supply. It would also be desirable if the apparatusand methods support large amounts of repetitive use at various operatingand standby durations and frequencies.

SUMMARY OF THE INVENTION

[0017] The present invention provides an electrochemical apparatuscomprising an electrochemical cell having first and second electrodesand electrolyte, such as an ion exchange membrane, disposed between thefirst and second electrodes, a power source for applying a voltagebetween the first and second electrodes, and means for automaticallyretracting one or more of the first and second electrodes out of contactwith the electrolyte. Optionally, the means for automatically retractingmay be passive, and the passive means for repetitively retracting may bea stored energy device. A stored energy device may be selected from aspring, gravity, hydraulic accumulator, pneumatic accumulator, orcombinations thereof.

[0018] The invention is well suited for use with one or more of thefirst and second electrodes includes material, such as lead dioxide,that is unstable or deactivates in the presence of the electrolytewithout applying a voltage. The invention is characterized in that thelead dioxide maintains its activity during repetitive cycling of thepower source.

[0019] The electrochemical apparatus may further comprise a pump fordelivering water to the electrochemical cell, wherein the means forretracting is a hydraulic actuator in fluid communication with thewater. Preferably, the electrolyte, such as an ion exchange membrane,and one of the electrodes, most preferably the cathode, are stationary.Where a lead-dioxide electrocatalyst is used, it may be desirable toinclude a lead removal device in fluid communication with theelectrochemical cell, wherein the lead removal device contains amaterial known to bind or adsorb lead ions, particulates or colloidalspecies. Such lead removal material may be selected from a zeolite,alumina, silica, or mixtures thereof, and may be in powdered orgranulated form.

[0020] In a preferred embodiment, the one or more of the first andsecond electrodes are retracted out of contact with the electrolyte whenno voltage is being applied between the first and second electrodes. Themeans for retracting the one or more electrodes may also include a guidemember to align the electrodes.

[0021] The electrochemical apparatus preferably also has a means forpositioning the first and second electrodes in contact with theelectrolyte. Preferably, the electrolyte is an ion exchange membrane,the first electrode is coupled to the means for positioning, and thefirst electrode has an electrocatalyst formed only on surfaces of thefirst electrode that are disposed to make contact with the ion exchangemembrane. In one embodiment, the second electrode is stationary and theion exchange membrane is secured onto the second electrode.

[0022] Exemplary means for positioning are selected from a hydraulicactuator, a pneumatic actuator, manual mechanical means, piezo-electricmeans, electric motor means, or combinations thereof, and preferablyprovide a compressive force against the ion exchange membrane generallybetween 5 and 100 psig, most preferably greater than 15 psig. Theapparatus maybe designed so that the means for retracting overcomes themeans for positioning when the power source is off, or so that the meansfor positioning overcomes the means for retracting when the power sourceis on.

[0023] The present invention also provides a method of operating anelectrochemical cell having first and second electrodes and electrolytedisposed between the first and second electrodes, comprisingautomatically separating one or more of the first and second electrodesfrom the electrolyte upon one or more standby conditions. The one ormore standby conditions may be selected from, but not limited to, avoltage of less than one Volt being applied between the first and secondelectrodes, expiration of a time period, an ozone concentration greaterthan a setpoint ozone concentration, contact pressure of less than 10psig, or combinations thereof. Furthermore, the method may includeautomatically positioning the one or more of the first and secondelectrodes into contact with the electrolyte upon one or more productionconditions. The one or more production conditions may be selected from avoltage greater than one Volt being applied between the first and secondelectrodes, expiration of a time period, an ozone concentration lessthan a setpoint ozone concentration, contact pressure greater than 10psig, or combinations thereof.

[0024] The preferred electrolyte is a polymer electrolyte membrane, andthe step of automatically positioning preferably comprises compressingthe one or more of the first and second electrodes against the polymerelectrolyte membrane with a compressive force between 5 and 100 psig,most preferably between 25 and 70 psig. While the method steps disclosedherein should generally not be limited to taking the steps in a givenorder, it is important when using a lead dioxide electrocatalyst, toapply a voltage between the first and second electrodes beforepositioning the one or more of the first and second electrodes intocontact with the electrolyte upon one or more production conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] So that the above recited features and advantages of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference to theembodiments thereof that are illustrated in the appended drawings. It isto be noted, however, that the appended drawings illustrate only typicalembodiments of this invention and are therefore not to be consideredlimiting of its scope, for the invention may admit to other equallyeffective embodiments.

[0026]FIG. 1 is a potential-pH equilibrium diagram for the system oflead-water at 25° C.

[0027]FIG. 2 is a single electrochemical cell capable of positioningelectrodes into compressed contact with an ion exchange membrane.

[0028]FIG. 3 is an alternative single electrochemical cell having a wavespring to retract an electrode away from the ion exchange membrane whenthere is no compression.

[0029]FIG. 4A is an electrochemical cell stack having a bipolar platebetween two cells of FIG. 3.

[0030]FIG. 4B is an electrochemical cell stack having two cells with acommon cathode.

[0031]FIG. 5A is a schematic side view of an electrochemical cell havingan anode coupled to a push rod, wherein an electrical solenoid actuatorwith a return spring controls the positioning of the push rod.

[0032]FIG. 5B is a schematic side view of the electrochemical cell ofFIG. 5A having a separate deionized water reservoir.

[0033]FIG. 5C is a schematic side view of the electrochemical cell ofFIG. 5B arranged to withdraw the electrode out of contact with a liquidelectrolyte.

[0034] FIGS. 6A-F illustrate exemplary means capable of actuating orpositioning an electrode to make contact with an electrolyte, the meansincluding an electrical solenoid with spring retraction (6A), a cam withspring retraction (6B), a hydraulic or pneumatic actuator (6C), a leadscrew (6D), rack and pinion (6E), and piezo-electric actuator (6F),respectively.

[0035] FIGS. 7A-B illustrate exemplary means for latching a push rod tosecure an electrode in contact with the PEM during the application ofelectricity.

[0036]FIG. 8 is a schematic side view of an experimental electrochemicalcell setup having an adjustable load and load cell for monitoring thecell operation as a function of compression force between the electrodeand the PEM.

[0037]FIG. 9 is a schematic side view of an electrochemical apparatushaving a water reservoir and a diaphragm allowing sealed movement of thepush rod.

[0038]FIG. 10A is a schematic side view of an alternativeelectrochemical apparatus having a hydraulically actuated anode.

[0039]FIG. 10B is a schematic side view of two electrochemicalcells/apparatus according to FIG. 10A, but having a common cathodetherebetween.

[0040]FIG. 11 is a schematic side view of an alternative electrochemicalapparatus having a process water reservoir and a pump that deliversprocess water to the electrochemical cell as well as to an integralhydraulic actuator.

[0041]FIG. 12 is a schematic side view of the electrochemical apparatusof FIG. 11 having the carbon filter and deionization bed relocated tothe pump inlet.

[0042] FIGS. 13A-C are schematic views of deionization beds arranged todisplay a color change that indicates the extent to which the beds arespent.

[0043]FIG. 14 is a schematic side view of an electrochemical apparatushaving a separate deionized water reservoir in fluid communication withthe anode.

[0044] FIGS. 15A-D are graphs of percent light absorption as a functionof time in seconds for electrochemical cells built according to FIG. 7and operated over many repetitive cycles.

[0045]FIG. 16 is a graph of cell voltage as a function of pressure inpsi for the electrochemical cell of FIG. 8.

[0046] FIGS. 17A-B are graphs of ozone current efficient in percent as afunction of time of a period in which the ozone generator is cycled onand off.

[0047] FIGS. 18A-C are perspective views of retractable electrodescoupled to a shaft, wherein the electrode has been modified to improvethe current distribution/collection across the face of the electrode.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention provides electrochemical apparatus andmethods that support periodic, non-steady state, or discontinuousoperation without suffering degradation of materials, includingelectrocatalysts, or loss of efficiency. The apparatus and methods donot require operator attention to verify that an electrical potentialacross the positive and negative electrodes, otherwise referred to as acell voltage, is continuously applied to the cell. The apparatus andmethods support large amounts of repetitive “on”/“off” cycles at variousoperating and standby durations and frequencies.

[0049] The basic structural unit of the electrochemical apparatus is anelectrochemical cell. Thus, an electrochemical apparatus can consist ofa single electrochemical cell or a plurality of electrochemical cells,either stacked in series in a bipolar filter press configuration orstacked in series and electrically connected in a monopolar format. Thestructural elements of an electrochemical cell consist of an anode, orpositive electrode, separated from a cathode, or negative electrode, byan ionically conducting electrolyte. If the electrolyte is a liquid, amicroporous separator may also be placed between the anode and cathode.The positive and negative electrodes are held spaced apart from eachother and contained, along with the electrolyte, in a container havingwalls which provide support and containment for the elements identified.The container also may have a plurality of input and output portsassociated with the supply of reactants and withdrawal of products fromboth the anodic region of the container as well as the cathodic regionof the container.

[0050] The anodic and cathodic electrodes may consist of a substratematerial on which is coated a suitable electrocatalyst layer. However,the substrate material may also function as the electrocatalyst itself.For many electrochemical processes, it is most suitable that theelectronically conducting anodic and cathodic electrode substratesshould be porous to allow access of liquid or gaseous reactants to theelectrocatalyst/electrolyte interface or withdrawal of liquid or gaseousproducts from the electrocatalyst/electrolyte interface.

[0051] Suitable anodic electrode substrates that are capable ofwithstanding high positive electrode potentials, aggressive electrolytes(concentrated aqueous mineral acids and mineral bases), and highlyoxidizing environments (ozone evolution) include porous titanium, poroustitanium suboxides (such as that produced by Atraverda Limited under thetrademark “EBONEX”), porous platinum, porous tungsten, porous tantalum,porous hafnium, porous niobium, porous zirconium, and combinationsthereof. The porous anodic substrates could be in the form of sinteredpowders or particles, compressed and sintered, or just compressedrandomly oriented fibers, woven or non-woven cloth or mesh, screens,felt materials, highly perforated metal sheets, or metal sheets withmicroetched holes. In the case of electrochemical ozone evolution,suitable anodic electrocatalyst layers include α-lead dioxide, β-leaddioxide, boron-doped diamond, platinum-tungsten alloys or mixtures,glassy carbon, fluorinated graphite, and platinum.

[0052] Suitable cathodic electrode substrates or suitable cathodicelectrode backing materials include porous metals selected fromstainless steels (in particular, 304 stainless steel and 316 stainlesssteel), nickel, nickel-chromium alloys, copper, titanium, titaniumsuboxides, tantalum, hafnium, niobium and zirconium. These cathodicsubstrates should be porous to allow the supply of liquid or gaseousreactants to the cathodic electrocatalyst/electrolyte interface orwithdrawal of liquid or gaseous products from the cathodicelectrocatalyst/electrolyte interface. Suitable porous cathodicsubstrates include sintered powders or particles, compressed andsintered or just compressed randomly oriented fibers, woven or non-wovencloth or mesh, screens, felts, highly perforated metal sheets, or metalsheets with microetched holes. In the case of electrochemical evolutionof ozone, a most suitable cathodic electrode substrate or electrodebacking material can be derived from porous stainless steel materials.Preferred cathodic electrocatalyst layers include platinum, palladium,gold, iridium, nickel, pyrolyzed carbon-supported cobalt phthalocyanine,graphite or carbon materials, ruthenium oxide, iridium oxide,ruthenium/iridium oxide, ruthenium/iridium/titanium oxide,carbon-supported platinum, carbon-supported palladium, and mixturesthereof.

[0053] Alternatively, the cathode may be a gas diffusion cathode, forexample comprising a polytetrafluoroethylene-bonded, semi-hydrophobiccatalyst layer supported on a hydrophobic gas diffusion layer. In oneembodiment of the present invention, the catalyst layer is comprised ofa proton exchange polymer, polytetrafluoroethylene polymer and anelectrocatalyst selected from platinum, palladium, gold, iridium,nickel, pyrolyzed carbon-supported cobalt phthalocyanine, graphite orcarbon materials, ruthenium oxide, iridium oxide, ruthenium/iridiumoxide, ruthenium/iridium/titanium oxide, carbon-supported platinum,carbon-supported palladium, and mixtures thereof. The gas diffusionlayer has a carbon cloth or carbon paper fiber impregnated with asintered mass derived from fine carbon powder and apolytetrafluoroethylene emulsion. This and other gas diffusion cathodesare suitable for air depolarization of the cathode, particularly inregard to open cathodes. U.S. Pat. Nos. 5,770,033 and 5,972,196 areincorporated by reference herein.

[0054] Electrolytes that are particularly useful in electrochemicalcells comprise aqueous solutions of mineral acids, aqueous solutions ofbases, aqueous solutions of salts, or aqueous solutions of saltscombined with either acids or bases. For the electrochemical productionof ozone in an electrolytic cell, it is particularly advantageous to usean electrolyte consisting of water and the acids or salts offluoroanions dissolved therein. The fluoroanion electrolytes are capableof producing high yields of ozone. Fluoroanions and in particular thehexafluoro-anions, are especially preferred. Aqueousfluoroanion-containing electrolytes are described in U.S. Pat. No.4,316,782, which patent is incorporated by reference herein.

[0055] A particular class of electrolytes suitable for use in accordancewith this invention may be any number of ion exchange polymers includingpolymers with cation exchange groups that are preferably selected fromthe group consisting of sulfonate, carboxylate, phosphonate, imide,sulfonimide, and sulfonamide groups. Various known cation exchangepolymers can be used including polymers and co-polymers oftrifluoroethylene, tetrafluoroethylene, styrene-divinylbenzene, α-, β₁-,β₂-trifluorostyrene, etc., in which cation exchange groups have beenintroduced. Polymeric electrolytes for use in accordance with thepresent invention are preferably highly fluorinated ion-exchangepolymers having sulfonate ion exchange groups. “Highly fluoroinated”means that at least 90% of the total number of univalent atoms in thepolymer are fluorine atoms. Most preferably, the polymer isperfluorinated sulfonic acid. Suitable solid polymer electrolytes basedon ion exchange polymers are described in U.S. Pat. No. 6,110,333 and6,042,958, which patents are incorporated by reference herein. Solidpolymer electrolytes based on perfluorinated cation exchange polymersare most suitable for electrochemical ozone evolution. This is becauseonly water, free of dissolved ionic species or suspended inorganic ororganic materials, needs to be added to an electrochemical cell. Thisavoids the degradation of electrochemical cell components by aggressiveelectrolytes and the entrainment of liquid electrolytes in evolvedgaseous ozone.

[0056] It is particularly preferred to utilize an ion exchange polymerthat is reinforced to improve the integrity and durability of themembrane. In particular, ultra-thin composite membranes below 50 μm inthickness and comprising proton exchange polymers incorporated into anexpanded porous polytetrafluoroethylene (PTFE) membrane are suitable foruse as the polymer electrolyte in the present invention. Such expandedPTFE-reinforced membranes are described in U.S. Pat. No. 5,547,551assigned to W.L. Gore & Associates Inc., which patent is herebyincorporated by reference. Another suitable membrane includes a poroussubstrate of randomly orientated individual fibres and an ion conductingpolymer embedded within the porous substrate. This individual fiberreinforced membrane is described in U.S. Pat. No. 6,042,958, whichpatent is hereby incorporated by reference. Other reinforced membranesthat are currently available or that will be developed in the future mayalso be suitable for use in accordance with the invention.

[0057] The proton exchange membrane placed between the anode and cathodeis made of a polymer material having sulfonate functional groupscontained on a fluorinated carbon backbone. Two such materials include a“NAFION” PEM having an equivalent weight of 1100 grams and a Dowexperimental PEM (XUS-13204.20) having an equivalent weight of 800grams. While “NAFION” 105, 115 and 117 will each operate satisfactorilyin the present invention, “NAFION” 117 is the preferred “NAFION”product. However, it is anticipated that a sulfonated polymer having anonfluorinated carbon backbone would be operable according to thepresent invention. Such a polymer might include polystyrene sulfonate.Additionally, such a material might be coated with a fluorinatedmaterial to increase its resistance to chemical attack. It is alsoanticipated that a proton exchange membrane made of a polymer materialhaving carboxylate functional groups attached to a fluorinated carbonbackbone would be operable according to the present invention. Examplesinclude those available from Tokuyama Soda Company under the trademark“NEOSEPT-F”, Asahi Glass Company under the trademark “FLEMION”, AsahiChemical Industry Company under the trademark “ACIPLEX-S” and TosohCorporation under the trademark “TOSFLEX IE-SA48.” Further, polymericsystems based on: perfluoro bis-sulfonimides(CF₃—[CF₂SO₂NHSO₂CF₂]_(n)—CF₃); perfluoro phosphonic acids, and thecorresponding carbocation acids would function satisfactorily as protonexchange membranes according to the present invention. The Dowexperimental PEM gives much superior performance than the “NAFION” PEMmaterials, which are manufactured by duPont. However, “NAFION” has beendetermined to be better for impregnating platinum electrodes.

[0058] A PEM-impregnated gas diffusion electrode can be hot-pressed ontoat least one side of a purified proton exchange membrane, using a Carverhot press, to produce a membrane and electrode (M&E) assembly. Thehot-pressing procedure involves placing a sandwich structure, consistingof the PEM and a PEM-impregnated gas diffusion electrode at one or bothsides of the PEM, between the platens of the press at approximately 100psi, where the platens having been previously heated to 100 degrees C.After the temperature of the platens has been raised to within apreselected range of between 125 degrees C. and 230 degrees C., apreselected pressure in the range 1,000 psi to 50,000 psi is applied tothe membrane and electrode assembly for a period of time varying from 15seconds to 150 seconds. The hot pressed M&E's should be immediatelyremoved from the hot press.

[0059] Preferred conditions for the preparation of M&E assemblies werefound to consist of a hot press temperature of 160 degrees C., a hotpressing time of 90 seconds and a hot press pressure in the range 3,000psi to 14,000 psi.

[0060] Lead dioxide anodes for use in the electrolytic cells of theinvention may be prepared by anodic deposition. The choice of anodicsubstrates on which lead dioxide is deposited are limited since mostmetals dissolve when deposition is attempted. However, the valve metals,such as titanium, titanium suboxides (such as that produced by AtraverdaLimited under the trademark “EBONEX”), platinum, tungsten, tantalum,niobium and hafnium are suitable as substrates for the anodes. Whentitanium, tungsten, niobium, hafnium or tantalum are utilized assubstrate materials, they are first platinized to eliminate passivationproblems sometimes encountered with the uncoated substrates. Theplatinizing process may include a predeposition chemical etch of thesubstrate material.

[0061] Carbon in the form of graphite may be used as a substrate;however, lead dioxide adherence is a particular problem if the carbonhas not been thoroughly degassed. The carbon is degassed by boiling inwater for some time followed by vacuum drying over a period of days.When degassed, adherence is greatly improved with respect to thermalstress. Vitreous or glassy carbon does not appear to have the adherenceproblem.

[0062] Platinum is the most convenient substrate material to work with,gives the most uniform deposits, and does not present any additionalproblems. Platinum is therefore typically the most suitable substratematerial for lead dioxide anodes. However, its high cost may make otherpreviously mentioned substrate materials more practical for commercialuse.

[0063] In any event, lead dioxide is plated onto substrates in a wellknown plating bath comprising essentially lead nitrate, sodiumperchlorate, copper nitrate, and a small amount of sodium fluoride andwater. The substrate material is set up as the anode in a plating bathwith a pH maintained between 2 and 4. Current densities of between 10and 400 milliamperes per square centimeter give bright, smooth andadherent lead dioxide deposits. Bath temperature is maintained attemperature in the range between 20 degrees C. and 70 degrees C. at alltimes during deposition. The deposition may be carried out with vigorousstirring of the electrolyte and rapid mechanical vibration of the anodeto give consistently fine granular deposits free from pinholes ornodules. A surface active agent may be added to the plating solution toreduce the likelihood of gas bubbles sticking to the anode surface.

[0064] A particularly suitable anodic electrode substrate and anodicelectrocatalyst for the electrochemical evolution of ozone, using eitheraqueous electrolytes or solid polymer electrolytes based on cationexchange polymers, is porous titanium coated with a layer of β-leaddioxide. To enhance the adhesion of the β-lead dioxide layer on theporous titanium substrate it has been found that the porous titaniumsubstrate should be suitably cleaned and chemically etched followed bythe deposition of a thin layer, or a flash coating, of metallic platinumon the porous titanium substrate immediately prior to theelectrodeposition of the β-lead dioxide electrocatalyst layer. However,in experimental work carried out by the inventors, it was found that thenature of the porous titanium substrate has a remarkable effect on theelectrochemical ozone generation efficiency and the lifetime of anelectrochemical cell for ozone evolution when a solid polymerelectrolyte based on a cation exchange polymer membrane, such asperfluorosulfonic acid, is used as the electrolyte.

The Retractable Electrode

[0065] The invention provides a means for positioning one or moreelectrodes into contact with electrolyte and means for retracting theone or more electrodes out of contact with the electrolyte. In a singlecell apparatus, it is preferred to have only one mobile electrode, i.e.,one positionable and retractable electrode, and one stationaryelectrode.

[0066] The means for positioning and means for retracting may be thesame device or different devices. It is preferred that the means forpositioning/retracting is designed to retract upon a given shutdowncondition, such as a voltage of less than one Volt being applied betweenthe first and second electrodes, expiration of a time period, an ozoneconcentration greater than a setpoint ozone concentration, contactpressure of less than 5 psig, and combinations thereof. Alternatively,the means for positioning/retracting may be designed to position the oneor more electrodes into contact with the electrolyte upon a givenproduction condition, such as a voltage greater than one Volt beingapplied between the first and second electrodes, expiration of a timeperiod, an ozone concentration less than a setpoint ozone concentration,contact pressure greater than 5 psig, and combinations thereof.

[0067] Using a lead dioxide anodic electrocatalyst, it is criticallyimportant to prevent the lead dioxide from contacting the acidicenvironment of the electrolyte while the electrical potential is off. Inaccordance with the present invention, there are three suitable modes ofstartup and shutdown. First, the anode must be retracted prior toremoving the applied potential, and a suitable potential must be appliedprior to contacting the anode to the electrolyte. For example, thevoltage may be applied for 30 seconds before the anode initiates contactwith the electrolyte and/or applied for 30 seconds following the anodebeing retracted out of contact with the electrolyte. Second, the voltagemay be turned off at the same time as the anode and electrolyte arebeing separated. Third, the applied electrical potential maybe kept“on”, wherein the contacting and retracting of the anode from theelectrolyte may act as a switch for turning the current “on” and “off”.

[0068] In accordance with the invention, it is also useful to providespecial startup and shutdown procedures that avoid abrupt changes in thepower applied. Accordingly, the procedure may include gradual ramping orincrementally stepping the power between a present value and a targetvalue. Such gradual or incremental increases or decreases in power maybe utilized each time the cell is cycled “on” and “off”. For instance,the current density through the cell may be stepped several times from0.15 Amps per square centimeter to eventually arrive at a final currentof 3 Amps per square centimeter. Furthermore, a special “initialstartup” profile maybe followed during the cell's first use in order toaccommodate certain one-time changes in cell conditions from theirshipment and storage condition to a fully operational condition, such asthe wetting of the membrane that must occur during a first use. In apreferred embodiment, the power may be adjusted so that the cell voltageremains within a given range of voltages most preferably between 3 voltsand 8 volts.

[0069] While the means for positioning and the means for retracting maybe active, passive or a combination of active and passive, it ispreferred that the means for retracting is passive and the means forpositioning is active. The term “active”, as used herein, means that acontinuous application of an outside force (electrical, hydraulic,pneumatic, piezoelectric) is necessary to secure the condition orposition of the device. For example, an electrical solenoid is an activedevice because a push rod connected to the solenoid is urged to adesired condition only while electrical power is maintained to thesolenoid. The term “passive”, as used herein, means that the conditionor position of the device will be maintained unless acted upon by anoutside force. For example, a wave spring or coil spring is a passivedevice because a push rod connected to the spring is urged to a desiredcondition unless the spring is overcome by an opposite outside force.The term “fail-safe”, as used herein, refers to the condition orposition that a device takes upon a particular failure, such as a lossof electricity.

[0070] In a preferred embodiment of the invention, the means forretracting is passive. Passive retraction is accomplished by providing amechanical stored energy device that maintains a bias on the actuatedelectrode toward the retracted condition or position, so that retractionoccurs automatically upon releasing the actuation force. The mechanicalstored energy device may be a spring, a pressurized fluid container,weight, and combinations thereof. In this manner, failure or shutdown ofthe electrochemical apparatus causes retraction of the electrode.

[0071] While positioning and retracting the one or more electrodes aregenerally directly opposite movements controlled by a guide member, theone or more electrodes may follow any of a number of paths. While thepreferred path is a linear path having a guide member that allows onlytranslational movement of the one or more electrodes, it also possibleto use an arcuate path having a guide member that allows only hingedmovement of the one or more electrodes. Regardless of the exactdirection of the path or the type of guide member involved, it isimportant that the one or more electrodes be positioned to maintainoperation of the entire active area of the cell, namely maintain theelectrode in fall face contact with the PEM and generally opposite theactive area of any opposing electrodes.

[0072] The guide member(s) may be provided in various forms, includingthose that guide the push rod and those that guide the electrode itself.Furthermore, the guides may be disposed through or around the electrodeor push rod, or consist only of a rigid connection with the positioningmeans. In addition to providing alignment of the electrodes and PEM, itis preferred that the guide member limit rotational and lateral movementof the electrode relative to the face of the PEM. Rotational and lateralmovement are undesirable not only because of potential physical damageto the PEM or electrocatalyst, but also because consistent realignmentof the electrocatalyst and PEM from one operating cycle to the nextallow any physical variation in the electrocatalyst and PEM surfaces toconform to each other as they do in a traditional cell where theelectrocatalyst and PEM are in constant compression. Consistentre-alignment of the electrocatalyst coated substrate and PEM from oneoperating cycle to the next is preferred in accordance with the presentinvention.

[0073] The electrolyte used in the electrochemical apparatus of thepresent invention may be either a liquid electrolyte or a solidelectrolyte (otherwise referred to as an ion exchange membrane), such asa PEM. Ion exchange membranes are preferred, because liquid electrolytesmust be maintained separate from the process water. While anelectrochemical cell will function with the electrodes merely contactingthe membrane, it is preferred to support the membrane on one of theelectrodes. This support may include securing the membrane to bestationary with respect to one of the electrodes or directly bonding orcasting the membrane onto one of the electrodes. An example of asuitable bonding procedure includes heating a perfluorinated sulfonicacid polymer membrane to about 160° C. under a pressure of up to 300psi, preferably for about 90 seconds. When using a lead dioxide anodicelectrocatalyst, the ion exchange membrane is secured to the cathode.

[0074] The cathode may be open to the air and have no direct supply ofwater. Such a cathode may be suitable for air depolarization as well asevaporative disposal of both the electroosmotic water and any productwater. However, since the membrane must be kept wet or moist in order tobe ionically conducting, a source of water must be provided to themembrane. Optionally, water may be provided from the anode side, eitheras liquid water or water vapor. Further, water may be provided from thecathode side for back diffusion into the membrane, either as liquidwater (no air depolarization) or water vapor. Even further, water may beprovided to an edge or other exposed area of the membrane so as to“wick” or absorb water into the membrane. Particularly in applicationswhere water of sufficient quality is scarce, it is anticipated that thehydration state of the membrane may be controlled or limited to makemore efficient use of water while accepting a reduction in the ionicconductivity of the membrane. Where the amount of water being suppliedto the membrane is limited, electroosmotic water and product water atthe cathode will be absorbed (back diffused) into the membrane.

[0075] While much of the description and drawings of the presentinvention refer to a single cell, the invention encompasses multiplecell arrangements, including both stacks of cells and side-by-sidearrays of cells. It should be recognized that both stacks andside-by-side arrays can be electronically coupled in either a parallelor series circuit depending upon the arrangement of electronicconductors and insulators. However, the configuration of a plurality ofcells in a side-by-side array may include a plurality of cells in thesame plane, a plurality of cells in two or more parallel planes, and aplurality of cells along a curvilinear surface. The commonly owned U.S.patent application Ser. No. 09/598,067 is incorporated by referenceherein.

[0076] The electrolytic cells may generate gas at any concentration, butthe gas concentration preferably comprises between about 1% and about18% by weight ozone in oxygen. Such electrolytic cells are described inU.S. Pat. No. 5,460,705 which description is incorporated by referenceherein. A fully passive electrolytic cell for producing ozone is mostpreferred for small scale point-of-use applications such as point-of-usewater treatment or built into equipment requiring ozone for sterilizing,disinfecting, decontaminating, washing, etc. The limited number ofmoving parts reduces the initial cost of the device and also reduces thepotential for failure and maintenance requirements of the device.

[0077] In the description of the Figures that follow, like numerals maybe used to refer to like elements among the Figures. The use of likenumerals for like elements means that the like elements have the samegeneral name and function, but like elements may have more or fewerfeatures in one Figure than the same element in another Figure. The useof like numerals is intended to more clearly describe the commonelements of the embodiments as they appear from Figure to Figure, and aparticular use of like numerals should not be taken as limiting thescope of the invention to specific features unless the descriptionexpressly states such limitations.

[0078]FIG. 2 is an exploded view of a single electrochemical cell 10capable of positioning two electrodes into compressed contact with anion exchange membrane. The cell 10 comprises an electronicallyconducting anode substrate 12 having an anodic electrocatalyst 14 formedon the surface facing the PEM 16. However, the anode substrate may alsofunction as both substrate and electrocatalyst. An electronicallyconducting cathode substrate 18 has a cathodic electrocatalyst 20 formedon the surface facing the PEM 16. However, the cathode substrate mayalso function as both substrate and electrocatalyst. The anode substrate12, cathode substrate 18 and PEM 16 are secured together by anelectrically nonconducting bolt 22 and nut 24. A power supply 26 has apositive terminal 28 and a negative terminal 29 placed in electroniccommunication with the anode substrate 12 and cathode substrate 18 viaelectronic conductors, respectively. The power supply applies thenecessary electrical potential (Volts) to drive the electrochemicalprocess. In one embodiment of the invention, the cell 10 is submersed inwater so that water is provided to and electrolyzed at the anodicelectrocatalyst to form a mixture of ozone/oxygen gas and water isprovided directly or indirectly to the PEM to support protonconductivity. Hydrogen gas or other cathodic product(s) is formed at thecathodic electrocatalyst.

[0079] The anode and cathode substrates are electronically conductingmetal or ceramic particles or fibers that yield a porous substrateusually in the form of a disc, square or rectangle. Exemplary substratesinclude, but are not limited to, woven felt, sintered metal, metalscreens, metal meshes, fabrics and the like.

[0080]FIG. 3 is an exploded view of an alternative singleelectrochemical cell 30 having a separation spring 32, such as a wavespring or wavy washer, to retract the anode substrate/electrocatalyst12, 14 away from the ion exchange membrane 16 when the compression isrelaxed, such as when the nut 24 is threaded away from the head of thebolt 22. The anode substrate 12 preferably has a recess 34 to receivethe compressed wave spring during operation and to maintain alignment(centering) of the wave spring with the anode substrate 12 so that thesubstrate 12 will be pushed away from contact with the PEM 16. Inapplications where it is important to minimize the retraction distance,it is beneficial to retract the substrate 12 an equal distance at allpoints over the substrate surface, such as with a substantiallytranslational movement.

[0081] While the retraction or separation distance may be any distanceat which the one or more electrodes are moved out of contact with thePEM, a controlled translational retraction can allow very smallretraction distances dependent upon the dimensional tolerances of theactuator and guide member, typically on the order of 1-5 millimeters,but certainly retractions of more than 5 millimeters and less than 1millimeter are possible. While the present invention does not reside inany particular separation distance, reference to a separation of “up to”a certain distance must avoid contact between the separated components,but may be as close as possible given dimensional tolerances of therelevant parts.

[0082] The term “retraction”, as used herein, means movement that causesseparation of components. The term “actuation”, as use herein, meansmovement that causes contact between components. Neither “retraction”nor “actuation” should be taken to imply whether a pushing or pullingforce is used to accomplish the separating or contacting movement unlesssuch pushing or pulling is expressly stated. In general, where theFigures show retraction accomplished by a pushing force, it should berecognized that a pulling force could be easily adapted to accomplishthe same movement. However, where springs are involved, as shown innumerous Figures herein, it is preferred, but not required, that thesprings be placed in compression rather than tension.

[0083]FIG. 4A is an exploded view of an electrochemical cell stack 40having a bipolar plate 42 disposed between two cells, such as a pair ofcells 30 from FIG. 3. In the manner shown, even a stack of cells caninclude a passive retraction mechanism (for example, one wave spring 32per cell) and an active actuation mechanism (for example, a bolt 22/nut24 combination). As shown in FIGS. 2-4, the bolt 22 also serves thefunction of a guide member that maintains alignment of the components.

[0084]FIG. 4B is an electrochemical cell stack 41 having two cells 43with a common cathode substrate 18 coupled to the negative terminal of apower source. The two cells 43 are mirror images, but in other respectsthe stack 41 is the same as the stack 40 of FIG. 4A. It is also possibleto operate a cell having a common anode and two cathodes.

[0085]FIG. 5A is a schematic side view of an electrochemical apparatus90 having an anode substrate 12/electrocatalyst 14 coupled to a push rod48, wherein the positioning of the push rod is controlled by anelectrical solenoid actuator 92 to compress the anode substrate12/electrocatalyst 14 against the PEM 16 and a return spring 46 toretract the anode. The cathode substrate 18/cathodic electrocatalyst20/PEM 16 assembly as well as the solenoid actuator 92 are secured in afixed relationship, such as by securing to a common housing 96, so thatmovement of the anode is achieved relative to the cathode/PEM simply byactivating the actuator. The cell is shown submersed in water 98 whilethe solenoid 92 is positioned out of the water. As used in the examplesbelow, a controller 94 is connected in the electronic circuit to providepower to the solenoid 92. The controller 94 may operate the apparatus 90in any number of ways based on a variety of conditions, such as a simpletimer specifying the “on” duration and frequency.

[0086]FIG. 5B is a schematic side view of the electrochemical apparatus90 of FIG. 7A having a separate deionized water reservoir 91 that ispreferably prepackaged deionized water. The water reservoir 91 isprovided in fluid communication with the housing 96 through a conduit93. The water reservoir 91 preferably contains deionized water toprovide high quality water to the apparatus and to eliminate the need toincorporate filtration and deionization devices into the apparatus. Thewater level in the reservoir 91 is controlled within certain limits,since the reservoir 91 will add water to the housing 96 whenever thewater level in the housing 96 falls below the level of the inlet conduit93 to allow a gas bubble to pass into the housing 91. The headspace 95above the water level allows phase separation of the ozone/oxygen gasfrom the water 98 so that the ozone/oxygen gas can then pass through theozone output 97, preferably having a valve (not shown) to regulate thewithdrawal of gas and/or maintain a backpressure.

[0087]FIG. 5C is a schematic side view of the electrochemical apparatus90 of FIG. 5B arranged to withdraw the electrode 12 out of contact witha liquid electrolyte 101. The apparatus is the same as in FIG. 5B exceptthat the ion exchange membrane 16 has been replaced by a liquidelectrolyte 101 and that the conduit 93 communicates with the housing 96to maintain the electrolyte level over the cathode 18, yet low enoughthat the anode 12 can be retracted out of contact with the electrolyte.

[0088] FIGS. 6A-F illustrate exemplary means capable of actuating orpositioning an electrode to make contact with electrolyte, the means forpositioning including: an electrical solenoid 44 for actuating the pushrod 48 upon throwing a switch or receiving a command from a controller50 in combination with a spring 46 for passively retracting the push rod(FIG. 6A); a cam 52 aligned to actuate the push rod 48 having a spring46 disposed between a retainer 54 and a collar 56 for providing passiveretraction of the push rod (FIG. 6B); a hydraulic or pneumatic actuator58 has a push rod 48 coupled to a piston 64, where the actuator 58includes a motive fluid feed conduit 60 for actuating and a motive fluidreturn conduit 62 for retracting the piston 64/push rod 48 (FIG. 6C); alead screw 68 push rod 48 and a lead screw motor 66 connected to powersource 26 through manual switches or an electronic controller 69 (FIG.6D); a rack 70/push rod 48 and pinion 72 (FIG. 6E, motor/power sourcenot shown); and a piezo-electric actuator 74 coupled to the push rod 48and activated by power source 26 through switch 50 (FIG. 6F). Otheractuating or positioning devices and variations of the foregoing devicesare deemed to be within the scope of the present invention.

[0089] FIGS. 7A-B are schematic diagrams of exemplary devices forlatching the push rod 48 in a position that secures an electrode (notshown) in contact with the PEM during the application of electricity. InFIG. 7A, the push rod 48 includes a latching notch 76 designed toreceive an extendable shaft 78 of a latching solenoid 80 uponapplication of electricity. In the absence of electrical power or uponthe occurrence of some other standby event, such as low cell voltage,the solenoid relaxes and the return spring 81 withdraws the shaft fromthe notch. If there is no longer an actuating force 82 being applied,then the spring 46 causes retraction of the push rod. In FIG. 7B, thepush rod 48 is coupled to an electromagnetic armature 83 that can beselectively secured to an electromagnet coil latch 84 coupled to a powersource 26 through a switch 50. Upon releasing the electromagnetic latch84, the spring 46 causes retraction of the push rod.

[0090] In FIGS. 6A-F and 7A-B it should be appreciated that in order toaccomplish movement of the push rod, the elements causing or preventingmovement of the push should be secured to the housing or otherstationary structure of the electrochemical apparatus.

[0091]FIG. 8 is a schematic side view of an experimental electrochemicalcell setup 100 having an adjustable load, such as a bolt 102 and spring104, and a load cell 106 for measuring the load and displaying orrecording the load with a meter 108. The ozone production efficiency canbe monitored as a function of compression force between the electrodeand the PEM. It is the compression force per unit area that is believedto be important to optimal cell performance.

[0092]FIG. 9 is a schematic side view of an electrochemical apparatus110 having a water reservoir or housing 112 and a sealing member, suchas diaphragm 114, allowing fluid-sealed movement of the push rod end 48a coupled to the positioning member 116 that is isolated from the waterand the push rod end 48 b coupled to the anode 12. Optionally, thesealing member may be piston rings, shaft seals and the like.

[0093] As shown, the cathode 18 and PEM 16 are stationarily secured atthe top and bottom to floor 118 and interior wall 120 portions of thehousing 112. The anode 12 is maintained in alignment with thecathode/PEM by a guide member comprising the surfaces 122, 124, whichare preferably circumferential about the anode 12. The apparatus 110 isalso shown having an anode chamber 126 isolated from a cathode chamber128. One benefit of the isolation is the separation of the anode gas(es)from the cathode gas(es). However, as a consequence of the isolation andthe electroosmotic flow of water from the anode to the cathode, it isbeneficial to have a conduit 129 in the apparatus 110 to allow thereturn of water from the cathode chamber 128 to the anode chamber 126without mixing the gas(es).

[0094] Optionally, the invention provides a unique gas destruct systemwhich can destruct waste hydrogen and/or ozone. The hydrogen is mixedwith oxygen (or air) and passed over a hydrogen destruction catalystproducing heat. The hot gases, including excess oxygen may then becombined with waste ozone and passed downstream over an ozonedestruction catalyst. Since the ozone generator continuously produceshydrogen, the heat from the hydrogen destruction maintains the ozonecatalyst at elevated temperatures to make the catalyst more active andto continuously dry the ozone destruct. In this manner, the ozonedestruct catalyst is maintained in a ready state for the destruction ofozone. Alternatively, the hydrogen destruct can provide high-grade heatthat may be used in other, unrelated processes, such as domestic hotwater heating. U.S. Pat. No. 5,989,407 and U.S. patent application Ser.No. 09/383,548 filed on Aug. 26, 1999 are incorporated by referenceherein.

[0095]FIG. 10A is a schematic side view of an alternativeelectrochemical apparatus 130 having a hydraulically actuated anode,wherein the motive fluid may be the process water or another fluid. Theanode 12 is coupled to the push rod 48 that has a piston 132 on theopposing end. The piston 132 is actuated by a fluid entering the pistonheadspace 134 to compress the return spring 136 and position the anodeinto compressed contact with the PEM 16. The apparatus has an optionaldiaphragm 138 attached around the push rod 48 to maintain isolation ofthe process water, which enters through the passage 140 and exits withgases produced through passage 142, from the motive fluid.

[0096] The cathode 18 is stationary with the PEM 16 secured to thecathode. Notably, there is no cathode chamber or reservoir around thecathode, but rather the cathode is open to the air and maybe referred toas “dry”. The open or exposed cathode may be suitable for airdepolarization as well as evaporative disposal of both theelectroosmotic water and any product water. Accordingly, there is nodirect supply of water to the cathode.

[0097]FIG. 10B is a schematic side view of two electrochemicalcells/apparatus according to FIG. 10A, but having a common cathodetherebetween. The common cathode 18 is coupled to a power source 26 asin FIG. 4B. However, the apparatus of FIG. 10B has two mobile anodes 12coupled to two means for positioning and retracting, which operate thesame as the individual means of FIG. 10A. The two means may be actuatedby the same or different motive fluids and may be actuated and retractedat the same or different moments. It is anticipated that the two mobileelectrodes may vary from each other in any of a number ofcharacteristics, for example catalyst loading, amount of active area,and types or concentrations of products produced. Optionally, the twoelectrodes may be operated independently to produce solutions that areoptimized for different uses, such as using one anode for producing an18 weight percent ozone solution for sanitizing countertops and usinganother anode for producing 2 weight percent ozone to cleanse skinburns.

[0098]FIG. 11 is a schematic side view of an alternative electrochemicalapparatus 150 having a process water reservoir 152 and a pump 154 thatdelivers process water 153 to the electrochemical cell (anode substrate12, PEM 16, cathode substrate 18) as well as to an integral hydraulicactuator. The hydraulic actuator is similar to that of FIG. 10, exceptthat the piston 132 is actuated with the process water 153. Theapparatus is also provided with a filter 154, preferably a carbonfilter, to remove, among other things, particulates, dissolved organiccompounds and heavy metals (also acting as an ozone destruct catalyst),a flow controller 156 (such as a flow restricting orifice), adeionization resin bed 158 to remove dissolved ions from the processwater 153, a lead removing unit 160 (such as a column of zeolite,alumina, silica or other materials known to bind or adsorb lead ions andparticulate or colloidal lead species), a venturi 162, and abackpressure control orifice 164. It should be recognized that the orderof the filter 154, flow controller 156 and deionization resin bed 158 isnot restricted.

[0099] In operation, water 153 from the reservoir 152 is provided to theinlet of pump 154 through a reservoir discharge conduit 165. The pumpdischarge conduit 166 provides high-pressure water for delivery to thepiston motive fluid chamber 134 or through the venturi 162 andbackpressure control orifice 164 back to the reservoir 152. The highpressure process water actuates the piston as in FIG. 10, but then theprocess water passes through the carbon filter, flow controller anddeionization resin bed on its way to the anode chamber. The deionizedwater supports electrolysis at the anode 12 as well as protonconductivity through the PEM 16 to the cathode 18. The electroosmoticwater passing to the cathode 18 may be recycled or discarded (i.e.,dumped into a drain or allowed to evaporate). However, the water that isnot used in the anode becomes ozonated and the water escapes the anodechamber along with the ozone/oxygen gas stream through discharge conduit167 and passes through the lead removal unit 160. Downstream of the leadremoval unit 160 the ozonated water and the ozone/oxygen gas stream aredrawn into the venturi and returned to the reservoir 152 where theconcentration of ozone is allowed to increase.

[0100] The startup of an electrochemical apparatus, such as theapparatus 150 of FIG. 11, may proceed in many ways, but it is preferredthat the startup include: (1) introducing process water into the waterreservoir, (2) applying a voltage between the first and secondelectrodes, (3) turning on the water pump, and (4) positioning themobile electrode into contact with the electrolyte, most preferably inthe order stated.

[0101]FIG. 12 is a schematic side view of the electrochemical apparatus150 of FIG. 11 having the carbon filter 154 and deionization bed 158relocated to the reservoir discharge conduit 165. Also, the flow controlorifice 156 is left between the motive fluid chamber 134 and the anodechamber in order to maintain or enhance the pressure differential actingupon the piston 132. It is also shown that the return spring 136 can bedisposed in tension.

[0102] FIGS. 13A-C are schematic views of deionization beds arranged tooutwardly display a color change that indicates to individual users ofthe device the extent to which the beds are exhausted. Suitabledeionization materials that change color upon exchanging ions includeMBD-12 and MBD-30 Self Indicating Mixed Bed Resins (available fromResintech, Inc. of Cherry Hill, N.J.) and IONAC NM-65 Indicator MixedBed Resin (available from Sybron Chemicals Inc. of Birmingham, N.J.).Such color changes may be due to the presence of an indicator dye in, onor around the deionization materials. While many arrangements of adeionization bed adjacent a clear sight glass are possible, it ispreferred that the deionization bed form an elongated column having ahigh aspect ratio (i.e., a length many times the width). In this manner,the deionization materials closest to the column inlet exchange ionsfirst and the material downstream will not be significantly used untilthe material upstream of it is fully exchanged. Therefore, there is afairly distinct region of the column that is carrying out thedeionization at any one time and this region propagates along the lengthof the column as the material gets used. Since a deionization materialwith a color change indicator is used, there is a color change thatpropagates along the column. By arranging the column in a manner where aplurality of serially spaced apart segments of the column pass under asight glass, a display can be provided that allows a rapid indication ofuse. Preferably, the sight glass is marked with a “replace deionizingbed” instruction adjacent one of the later column segments viewablethrough the sight glass. While the foregoing arrangement has beendescribed with regard to a deionization bed, a similar arrangement,color indicator and sight glass maybe used to prepare a lead removalunit.

[0103] In FIG. 13A, a side view shows that the deionization column 170is arranged in an elongated serpentine pattern having an inlet 172, anoutlet 174, deionization material 176 disposed there between, and asight glass 178 adjacent one end of the serpentine. FIG. 13B is an endview of the column 170 showing the display formed by the sight glasses.For example, an individual user would quickly notice that the presentcolumn was two-fifths spent and that the column should be replaced whenthe column becomes four-fifths spent in order to prevent breakthrough ofions that could then reach and damage the electrocatalysts or the PEM.While the display is shown as a segmented array of sight glasses it isequally suitable to have a continuous sight glass along the end. FIG.13C is a side view of an alternative column arranged in an spiralingpattern having an inlet 172, an outlet 174, deionization material 176,and a sight glass 178 extending over downstream segments of the column.While the segments here do not represent equal fractions of the column,the display is still effective to instruct the individual user when tochange out the column with a new column.

[0104]FIG. 14 is a schematic side view of an electrochemical apparatususing deionized water from a reservoir 91 rather than using processwater from reservoir 152. As with FIGS. 7B-C, the use of prepackageddeionized water 91 eliminates the threat of contaminating the anode andPEM such that filtration and deionization devices are not needed withinthe apparatus. Here, the process water 153 is pressurized by pump 154and delivered to the back of the piston 132 for actuating the mobileelectrode and through the venturi 162 to draw ozone gas into the processwater. Preferably, the anode chamber is arranged with the water conduit93 such that the level of deionized water remains below the ozone exitport 169. It is also preferred that the anode chamber have sufficientheadspace to allow for phase separation of the ozone/oxygen gas from thewater, such that only the gas phase is drawn through port 169 to theventuri 162. A seal or diaphragm is provided around the push rod 48 toprevent passage of the pressurized process fluid acting upon the pistonfrom getting into the anode chamber. As shown, the diaphragm 171 definesthe upper limit of the anode chamber.

[0105] FIGS. 18A-C are perspective views of retractable electrodescoupled to a shaft, wherein the electrode has been modified to improvethe current distribution/collection across the face of the electrode.FIG. 18A illustrates an electrode 200 having a set of electronicallyconducting ribs 206, preferably metal, that are formed into a radialpattern on the back surface of the anode substrate 204 in order toimprove current distribution or collection from the electronicallyconducting shaft 202 across the face of the electrode substrate 204.This design improves current distribution without blocking the surfacearea of the anode substrate or increasing the thickness of the porousanode substrate. FIG. 18B illustrates an electrode 210 having a set offully embedded electronically conducting members 208 disposed radiallyfrom the shaft 202. In both FIGS. 18A and 18B, the electronicallyconducting members 206, 208 are formed within the porous substrate 204.Preferably, the electronically conducting members are disposed within ametal powder and pressed together under substantial pressure to form a“green body.” The green body is then transferred into a furnace forsintering the substrate 204. FIG. 18C illustrates an electrode 220having a less preferred conical substrate 224 coupled to the shaft 222,wherein the increased thickness of the substrate increases the currentdistribution or collection across the face of the anode. Unfortunately,the increased thickness also increases the distance that anode reactantsand products must diffuse.

EXAMPLE 1

[0106] Porous titanium substrates, namely pieces of a woven titaniumcloth (150×150 per inch, clean, 0.0027″ wire diameter, twill weave,35.4% open area; Unique Wire Weave, Hillside, N.J. 07205), werepretreated and subsequently electroplated with β-lead dioxide. A numberof these plead dioxide-coated titanium cloths were used in anelectrochemical cell incorporating a commercially available protonexchange polymer membrane (sold under the trade name Nafion®, by E.I. duPont de Nemours and Company, Wilmington, Del. 19898), which is aperfluorosulfonic acid solid polymer electrolyte, and tested using anapparatus described in U.S. Pat. No. 5,460,705 commonly owned by theapplicant. In some cases, the β-lead dioxide-coated titanium cloths weremechanically pressed against one side of a proton exchange membranesample simply by means of clamping together the endplates of theelectrochemical cell. In other cases, the β-lead dioxide-coated titaniumcloths were hot pressed onto one side of similar samples of a protonexchange membrane. Hot pressing involved placing a sandwich structure,consisting of the cation exchange membrane, the β-lead dioxide-coatedtitanium cloth anode electrode, and a platinum-supported carboncatalyzed carbon cloth gas diffusion electrode on either side of themembrane between the platens of a hot press preheated to 100° C. andpressing at approximately 100 psi. The temperature of the platens wasthen raised to 120° C. and a pressure of 2,500 psi was applied for 90seconds.

[0107] On testing the performance of electrochemical cells containingβ-lead dioxide-coated titanium cloth electrodes bonded to cationexchange polymer membranes by either method, it was found that the ozonegas content in the evolved ozone/oxygen gas stream decreased from aninitially high value of 12-15 wt % to a value of the order of 1-2 wt %over a period of time of the order of 12-24 hours. Further, cellvoltages decreased from initially high values of the order of 4-6 voltsto a value of the order of 1-2 volts. In addition, upon dismantlingtested electrochemical cells that contained β-lead dioxide-coatedtitanium cloth as the anode substrate/anode electrocatalyst material,the surface of the proton exchange polymer membrane in contact with theβ-lead dioxide electrocatalyst layer had regions covered with a milkywhite liquid substance. The surface of the proton exchange polymermembrane in contact with the platinum-supported carbon cathodicelectrocatalyst layer displayed dendrithic or fractal-like growths of amaterial within the membrane.

[0108] While the nature of these materials on the surfaces of the protonexchange polymer membranes were not determined, it is proposed that thefollowing processes took place on testing these electrochemical cellsfor electrochemical ozone evolution. The individual wire strands thatmade up each woven titanium cloth sample was electroplated with leaddioxide over the entire circumference of the cylindrically shaped wirestrands. However, when the β-lead dioxide-coated titanium cloth sampleswere bonded to the surfaces of proton exchange membrane samples, eitherby mechanical pressing on clamping the end plates or by hot pressing,only a fraction of the entire surface area of the β-lead dioxideelectrocatalyst layer was in contact and embedded into the protonexchange polymer membrane material.

[0109] On operating an electrochemical cell containing such an anodicsubstrate/electrocatalyst layer, parts of the β-lead dioxideelectrocatalyst layer not in contact with the proton exchange polymermembrane slowly dissolved in the presence of the highly acidicenvironment that exists at the anode surface under electrochemical ozoneevolution conditions. Some of the dissolved β-lead dioxide, in the formof Pb²⁺ cations, migrated through the cation exchange polymer membraneto the surface of the cathode, under the presence of the appliedelectric field, where they were reduced to metallic lead atoms.Gradually, build up of atom-upon-atom of lead metal gave rise to adendrithic growth of electrodeposited lead metal from the surface of thecathode through the proton conducting channels that are known to existin proton exchange polymer membranes to the surface of the anode.Eventually, the proton exchange polymer membrane became a mixedionic/electronic conductor with increasing electronic conductivitycharacter as the time of electrochemical ozone evolution increased. Thisaccounts for the decrease in cell voltage observed with increasing timeof electrolysis.

[0110] Because the woven titanium cloth consisted of fine cylindricaltitanium wires, subsequent contact of these β-lead dioxide-coatedtitanium wires with the surface of the proton exchange polymer membraneled to localized point contacts embedded into the surface of themembrane, particularly at points corresponding to the overlap of thewoven wires. Thus, although the average current density applied to theelectrochemical cells on carrying out the various tests were 1 A cm⁻² onaverage, it is very likely that the local real current density appliedat the point contacts could be of the order of 5-10 A cm⁻². Thecombination of heating effects (associated with the high local currentdensity) with the highly oxidizing environment (associated with ozoneevolution) gave rise to local degradation of the proton exchangemembrane. This is in keeping with the observation of a milky whiteliquid substance on the surface of the proton exchange polymer membranein contact with the β-anodic lead dioxide electrocatalyst layer. In allcases, electrochemical tests involving β-lead dioxide-coated titaniumcloth anodes were carried out using deionized water circulated between areservoir and the electrochemical cell, where the temperature of thewater was maintained at 30±3° C.

EXAMPLE 2

[0111] Another type of porous titanium substrates, namely sinteredporous titanium substrates derived from the sintering of regular shapedtitanium powders (e.g., spheres) or irregular shaped titanium particlesunder high temperature and pressure in an inert gas environment andavailable from Astro Met, Inc., Cincinnati, Ohio 45215 (100-80/120 and100-45/60; 5.5″×11″×0.050″ sheets) and Mott Corporation, Farmington,Conn. 06032 (Mott 40 micron and Mott 20 micron), respectively, wereused. The sintered porous titanium substrates were pretreated andsubsequently electroplated with β-lead dioxide as described above forthe titanium cloth samples. The β-lead dioxide-coated sintered poroustitanium substrates were mechanically pressed against one side ofsamples of a proton exchange polymer membrane (Nafion®) on clamping theendplates of an electrochemical cell together. They were tested underidentical conditions to those utilized for the β-lead dioxide-coatedtitanium cloth anodic substrates. The thickness of the porous titaniumsubstrates was in the range 0.040″-0.075″ and it was observed that thesesubstrates had very flat parallel surfaces. β-lead dioxide was depositedon only one surface of the sintered porous titanium substrates whichformed a uniform coating covering the whole surface of each substrate.

[0112] On testing β-lead dioxide-coated sintered porous titaniumsubstrates for electrochemical ozone evolution, it was found thatelectrochemical cells containing these anodic substrates/electrocatalystlayers could produce ozone at high concentrations of the order of 12 to15 wt % for seemingly indefinite periods of time, so long as suchelectrochemical cells remained under compression and an applied currentdensity of 1.0-1.6 A cm⁻² was impressed on the electrodes from anexternal DC power source. Cell voltages of 3.5-5.5 V were observed onflowing deionized water between the electrochemical cell and a reservoirat a temperature of 30±3° C. The unexpected result of the continuousproduction of high weight percent ozone for an extended period of timeis attributed to the fact that the sintered porous titanium substrateshave flat planar surfaces. Thus, the β-lead dioxide layer on suchsurfaces is also flat resulting in all of the exposed surface area ofthe Plead dioxide layer being in contact with the surface of the protonexchange polymer membrane, and under electrochemical operatingconditions, having a voltage greater than 3.0 V applied across the pleaddioxide/proton exchange polymer membrane interface. As indicated in FIG.1, under such circumstances, β-lead dioxide should be stableindefinitely.

EXAMPLE 3

[0113] β-lead dioxide coated sintered porous titanium substrates weresubjected to multiple applied current density “on”/“off” events, leadingto a gradual lowering of the ozone current efficiency. For coatedsubstrates that were maintained continuously in compression with theproton exchange polymer membrane, both in the case when the appliedcurrent density was “on” and when the applied current density was “off,”the effect of four applied current density “on”/“off” events on theozone current efficiency for an electrochemical cell initially producingozone at a current efficiency of 14.5 (corresponding to a concentrationof 14.5 wt %) is presented in FIGS. 17A-B. It was further observed thatthe dramatic effect of applied current density “on”/“off” events onozone current efficiency was more pronounced for electrodes having lowelectrocatalyst loadings of β-lead dioxide. For instance, for β-leaddioxide loadings of 5-10 mg cm⁻², 2-3 applied current density “on”/“off”events reduced the ozone production capability of the electrochemicalcell from 10-12 wt % to less than 2 wt %. For an electrode with a β-leaddioxide loading of 80 mg cm⁻², an ozone production capability of theorder of 5 wt % was obtained after 9 applied current density “on”/“off”events.

[0114] Degradation in ozone production performance as a result of timeintervals while no current density is impressed upon the electrodes issuggested by the data presented in FIG. 1. This figure clearly showsthat for the lead-water system at low electrode potentials, that is,when no anodic current is flowing through the electrode/electrolyteinterface, Pb²⁺ ions are the most stable species in acidic environments.Maintaining a β-lead dioxide-coated sintered porous titanium substratein contact with an acidic proton exchange polymer membrane when nocurrent is flowing through an electrochemical cell will give rise todegradation of the β-lead dioxide electrocatalyst layer whichsubsequently hinders, or reduces, its ability to evolve ozone gas onreimpressing a current between the β-lead dioxide-coated anode and acathode.

[0115] Under the conditions of no applied electric field, that is, whenthe current density impressed on the electrodes is turned “off,”dissolution/precipitation processes involving PbO₂/Pb²⁺ are likely totake place at the β-lead dioxide/proton exchange polymer membraneinterface. In the absence of an applied electric field during current“off” events, there is no driving force for the migration of Pb²⁺ ionsinto the proton conducting polymer membrane towards the surface of thecathode unlike the situation described above for the β-leaddioxide-coated titanium cloth.

EXAMPLE 4

[0116] An experimental setup was prepared including four electrochemicalcells to test whether the removal of β-lead dioxide-coated porous anodicsubstrates from being in contact with proton conducting polymermembranes, during time intervals when no current is flowing between theanode and cathode, would significantly increase the lifetime of suchelectrochemical cells and maintain high ozone production rates when anapplied current density is reimpressed on the electrodes after a current“off” event. However, this solution is only applicable to porous anodicsubstrates that have flat planar surfaces as described above in thesecond example which involved the use of sintered porous titaniumsubstrates. The proposed solution, which is the basis of the inventiondisclosed in this patent application, will not be effective in the caseof porous anodic substrates that have only portions of the surface areaof a layer, or regions of the surface of a layer, of β-lead dioxideanodic electrocatalyst in contact with the proton exchange polymermembrane when the electrocatalyst-coated porous substrate and themembrane are compressed together in an electrochemical cell.

[0117] Porous anodic substrates that would be ineffective are those thathave a relatively small thickness (less than 0.010″ thick) and have alayer of β-lead dioxide electrocatalyst material on a front or firstsurface, around the entire perimeter of fine wires, on walls of largepores readily accessible to water and on a back or second surface. Arepresentative example of such porous substrates was described above inthe first example and involved the use of porous woven titanium cloth.Other ineffective porous substrates would include non-woven cloths,woven or non-woven meshes, screens, perforated thin metal sheets, orthin metal sheets with microetched holes. However, if the β-lead dioxideelectrocatalyst layer is deposited on only those regions of the surface,segments of the surface or portions of the exposed surface area of wovenor non-woven cloths, woven or non-woven meshes, screens, perforated thinmetal sheets, or thin metal sheets with microetched holes that are incontact with a proton exchange polymer membrane when such plated porousanodic substrates and membrane specimens are under compression inelectrochemical cells, then the proposed solution is as effective forthese substrates as it is for sintered porous metal or ceramicsubstrates described in the second example above.

[0118] An apparatus and method for retracting a β-lead dioxide-coatedporous anodic substrate from making contact with a proton conductingpolymer membrane and for subsequently having the ability n of placingsuch a β-lead dioxide-coated porous anodic substrate back in contactwith the proton conducting polymer membrane was prepared in accordancewith FIG. 7. In particular, the apparatus and method of the inventionmust be capable of retracting all of the exposed surface area of theβ-lead dioxide coating on a porous anodic substrate from making contactwith a proton exchange polymer membrane specimen in an electrochemicalcell during a current “off” event. Similarly, the apparatus and methodof the invention must be capable of placing all of the exposed surfacearea of the β-lead dioxide coating on a porous anodic substrate incontact with a proton exchange polymer membrane specimen in anelectrochemical cell during a current “on” event.

[0119] The cathode and PEM were stationary with only the porous titaniumanode substrate and lead dioxide electrocatalyst coupled to the end ofan electrically operated solenoid actuator. The solenoid actuator pushedthe anode substrate/electrocatalyst into compressed contact with the PEMand a pair of springs raised the anode substrate/electrocatalyst awayfrom the PEM. A controller was used to control each of the fourelectrochemical cells at a given duration and frequency of operation.Each of the cells was operated without switching off the power. However,the cells were turned “off” by retracting the anode out of contact withthe PEM/cathode, since the non-ionically conducting deionized watereffectively provided an open circuit. Cell #1 was operated in a cycle of1.5 minutes “on” and 1.5 minutes “off”. Cell #2 was operated in a cycleof 25 minutes “on” and 10 minutes “off”. Cell #3 was operated in a cycleof 25 minutes “on” and 2 hours “off”. Cell #4 was operated in a cycle of26 minutes “on” and 24 hours “off”. A control cell was operated in whichthe power was switched off during periods when the anode was retracted,but the results showed no significant difference in performance relativeto cells having the power on continuously.

[0120] The ozone gas concentration produced by each of the fourelectrochemical cells was measured using an Ocean Optics UV absorptionsystem and software to monitor the absorption of UV light by dissolvedozone in the deionized water surrounding the cell. FIGS. 15A-D show thelight absorbance that was measured periodically after large numbers ofoperating cycles had been performed for cells 1-4, respectively. Thelegend in each figure indicates the number of operating cycles at whichthe dissolved ozone concentration was tested. For each test, the figuresplot percentage light absorption as a function of time in seconds for aperiod of about 1500 seconds. Each of the charts in FIGS. 15A-D showthat very little decline in ozone production occurred despite 62,218;63,468; 4,826 and 1,412 operating cycles in cells 1-4, respectively.

EXAMPLE 5

[0121] An electrochemical cell was prepared in accordance with FIG. 8and the cell voltage was measured as the compression between theelectrodes was varied between about 10 psi and about 260 psi. FIG. 16 isa graph of the resulting cell voltage as a function of pressure in psifor the electrochemical cell. The graph shows that cell voltage declinesrapidly with increasing pressure up to a pressure of about 50 psi. Atpressures above 50 psi, additional pressure produced very little declinein cell voltage.

[0122] While the foregoing is directed to the preferred embodiment ofthe present invention, other and further embodiments of the inventionmay be devised without departing from the basic scope thereof, and thescope thereof is determined by the claims that follow.

What is claimed is:
 1. An electrochemical apparatus, comprising: anelectrochemical cell having first and second electrodes and electrolytedisposed between the first and second electrodes, a power source forapplying a voltage between the first and second electrodes, and meansfor automatically retracting one or more of the first and secondelectrodes out of contact with the electrolyte.
 2. The electrochemicalapparatus of claim 1, wherein the means for automatically retracting ispassive.
 3. The electrochemical apparatus of claim 2, wherein thepassive means for repetitively retracting is a stored energy device. 4.The electrochemical apparatus of claim 3, wherein the stored energydevice is selected from a spring, gravity, hydraulic accumulator,pneumatic accumulator, or combinations thereof.
 5. The electrochemicalapparatus of claim 1, wherein the electrolyte is an ion exchangemembrane.
 6. The electrochemical apparatus of claim 1, wherein the oneor more of the first and second electrodes includes material that isunstable or deactivates in the presence of the electrolyte withoutapplying a voltage.
 7. The electrochemical apparatus of claim 6, whereinthe material is lead dioxide.
 8. The electrochemical apparatus of claim7, characterized in that the lead dioxide maintains its activity duringrepetitive cycling of the power source.
 9. The electrochemical apparatusof claim 1, further comprising: a pump for delivering water to theelectrochemical cell, wherein the means for retracting is a hydraulicactuator in fluid communication with the water.
 10. The electrochemicalapparatus of claim 1, wherein the electrolyte and one of the electrodesare stationary.
 11. The electrochemical apparatus of claim 10, whereinthe electrolyte is an ion exchange membrane.
 12. The electrochemicalapparatus of claim 11, wherein the stationary electrode is a cathode.13. The electrochemical apparatus of claim 1, wherein theelectrochemical cell is a stack of electrochemical cells.
 14. Theelectrochemical apparatus of claim 1, further comprising: alead-containing catalyst disposed on one or more of the first and secondelectrodes; and a lead removal device in fluid communication with theelectrochemical cell.
 15. The electrochemical apparatus of claim 14,wherein the lead removal device contains a material known to bind oradsorb lead ions, particulates or colloidal species.
 16. Theelectrochemical apparatus of claim 15, wherein the material is selectedfrom a zeolite, alumina, silica, or mixtures thereof.
 17. Theelectrochemical apparatus of claim 15, wherein the material is inpowdered or granulated form.
 18. The electrochemical apparatus of claim1, wherein the one or more of the first and second electrodes areretracted out of contact with the electrolyte when no voltage is beingapplied between the first and second electrodes.
 19. The electrochemicalapparatus of claim 1, wherein the means for retracting the one or moreelectrodes further comprises a guide member to align the electrodes. 20.The electrochemical apparatus of claim 1, wherein the means forretracting the electrodes is coupled to the one or more of the first andsecond electrodes by a positioning rod.
 21. The electrochemicalapparatus of claim 20, further comprising an electrode chamber having aliquid impermeable diaphragm sealing the chamber and moving along withthe positioning rod.
 22. The electrochemical apparatus of claim 9,further comprising means for introducing ozone into a separate system.23. The electrochemical apparatus of claim 22, wherein the ozonecomprises dissolved ozone in water, an ozone/oxygen gas stream, orcombinations thereof.
 24. The electrochemical apparatus of claim 1,further comprising: means for positioning the first and secondelectrodes in contact with the electrolyte.
 25. The electrochemicalapparatus of claim 24, wherein the electrolyte is an ion exchangemembrane, and wherein the first electrode is coupled to the means forpositioning and the first electrode has an electrocatalyst formed onlyon surfaces of the first electrode that are disposed to make contactwith the ion exchange membrane.
 26. The electrochemical apparatus ofclaim 25, wherein the second electrode is stationary.
 27. Theelectrochemical apparatus of claim 26, wherein the ion exchange membraneis secured onto the second electrode.
 28. The electrochemical apparatusof claim 24, wherein the means for positioning is selected from ahydraulic actuator, a pneumatic actuator, manual mechanical means,piezo-electric means, electric motor means, or combinations thereof. 29.The electrochemical apparatus of claim 24, further comprising: a pumpfor delivering water to the electrochemical cell, wherein the means forpositioning is a hydraulic actuator in fluid communication with thewater.
 30. The electrochemical apparatus of claim 24, wherein the meansfor positioning provides a compressive force against the ion exchangemembrane generally greater than 15 psig.
 31. The electrochemicalapparatus of claim 24, wherein the compressive force is between 5 and100 psig.
 32. The electrochemical apparatus of claim 24, wherein themeans for retracting overcomes the means for positioning when the powersource is off.
 33. The electrochemical apparatus of claim 24, whereinthe means for positioning overcomes the means for retracting when thepower source is on.
 34. The electrochemical apparatus of claim 24,wherein the means for positioning the electrodes further comprises aguide member to align the electrodes.
 35. The electrochemical apparatusof claim 24, wherein the means for positioning the electrodes is coupledto the one or more of the first and second electrodes by a positioningrod.
 36. The electrochemical apparatus of claim 35, further comprisingan electrode chamber having a liquid impermeable diaphragm sealing thechamber and moving along with the positioning rod.
 37. Theelectrochemical apparatus of claim 35, wherein the positioning rodcomprises an electronic conductor communicating between a voltage sourceand the one or more of the first and second electrodes.
 38. Theelectrochemical apparatus of claim 24, further comprising a waterreservoir in fluid communication with an inlet to the pump and in fluidcommunication with an outlet from the electrochemical cell.
 39. Theelectrochemical apparatus of claim 38, further comprising arecirculation conduit from an outlet of the pump back to the waterreservoir.
 40. The electrochemical apparatus of claim 39, furthercomprising means for apportioning the amount of water pumped to theelectrochemical cell and the amount of water recirculated back to thewater reservoir.
 41. The electrochemical apparatus of claim 24, furthercomprising an ion exchange bed disposed upstream of the electrochemicalcell.
 42. The electrochemical apparatus of claim 41, further comprisingan ozone destruct catalyst upstream of the ion exchange bed.
 43. Theelectrochemical apparatus of claim 24, wherein the electrochemical cellis a fuel cell.
 44. An electrochemical apparatus, comprising: anelectrochemical cell having first and second electrodes and electrolytedisposed between the first and second electrodes, a power source forapplying a voltage between the first and second electrodes, and meansfor passively retracting one or more of the first and second electrodesout of contact with the electrolyte.
 45. An electrochemical apparatus,comprising: an electrochemical cell having first and second electrodesand electrolyte disposed between the first and second electrodes, apower source for applying a voltage between the first and secondelectrodes, means for selectively positioning one or more of the firstand second electrodes into contact with the electrolyte; and means forretracting the one or more of the first and second electrodes out ofcontact with the electrolyte when the means for selectively positioningis turned off.
 46. A method of operating an electrochemical cell havingfirst and second electrodes and electrolyte disposed between the firstand second electrodes, comprising: (a) automatically separating one ormore of the first and second electrodes from the electrolyte upon one ormore standby conditions.
 47. The method of claim 46, wherein the one ormore standby conditions is selected from a voltage of less than one Voltbeing applied between the first and second electrodes, expiration of atime period, an ozone concentration greater than a setpoint ozoneconcentration, contact pressure of less than 10 psig, or combinationsthereof.
 48. The method of claim 46, further comprising: (b)automatically positioning the one or more of the first and secondelectrodes into contact with the electrolyte upon one or more productionconditions.
 49. The method of claim 48, wherein the one or moreproduction conditions is selected from a voltage greater than one Voltbeing applied between the first and second electrodes, expiration of atime period, an ozone concentration less than a setpoint ozoneconcentration, contact pressure greater than 10 psig, or combinationsthereof.
 50. The method of claim 48, wherein the electrolyte is apolymer electrolyte membrane, and wherein the step of automaticallypositioning comprises compressing the one or more of the first andsecond electrodes against the polymer electrolyte membrane with acompressive force between 5 and 100 psig.
 51. The method of claim 50,wherein the compressive force is between 25 and 70 psig.
 52. The methodof claim 48, further comprising: applying a voltage between the firstand second electrodes.
 53. The method of claim 52, further comprising:turning on a water pump.
 54. The method of claim 53, further comprising:automatically positioning the one or more of the first and secondelectrodes into contact with the electrolyte upon one or more productionconditions.
 55. An electrode, comprising: a porous metal substratehaving a substantially nonporous metal current collector is at leastpartially embedded within the substrate; and an electrical connectorcoupled to the metal current collector and extending from the porousmetal substrate.
 56. The electrode of claim 55, wherein the porous metalsubstrate is sintered around metal current collector.
 57. The electrodeof claim 56, wherein the metal current collector is entirely embeddedwithin the porous metal substrate.
 58. The electrode of claim 55,wherein the electrical connector forms part of a shaft coupled to theporous metal substrate.
 59. The electrode of claim 58, characterized inthat the porous metal substrate may be moved by actuating the shaft. 60.A method for controlling the voltage applied to an ozone generatorincluding an anode substrate with a lead dioxide anodic electrocatalyst,a cathode, and a proton exchange membrane in contact between the leaddioxide and the cathode, the method comprising: separating the leaddioxide out of contact with the proton exchange membrane; then waitingfor an interval of time; and then reducing the voltage.
 61. The methodof claim 60, wherein the step of reducing the voltage comprises turningoff the voltage.
 62. The method of claim 60, wherein the voltage isreduced to a setpoint voltage for maintenance of the lead dioxide anodicelectrocatalyst.
 63. A method for controlling the voltage applied to anozone generator including an anode substrate with a lead dioxide anodicelectrocatalyst, a cathode, and a proton exchange membrane in contactbetween the lead dioxide and the cathode, the method occurring while thelead dioxide is maintained in contact with the proton exchange membrane,the method comprising: determining the present value of a parameterselected from cell voltage and cell current identifying a setpoint forthe parameter; and adjusting the power applied to the ozone generator sothat the parameter is changed from the present value to the setpointover a period of time.
 64. The method of claim 63, wherein the power isadjusted gradually until reaching the setpoint for the parameter. 65.The method of claim 63, wherein the power is adjusted in incrementsuntil reaching the setpoint for the parameter.
 66. A method forcontrolling the voltage applied to an ozone generator including an anodesubstrate with a lead dioxide anodic electrocatalyst, a cathode, and aproton exchange membrane in contact between the lead dioxide and thecathode, the method comprising: separating the lead dioxide out ofcontact with the proton exchange membrane if the voltage between theanode substrate and the cathode becomes less than a setpoint voltage.67. The method of claim 66, wherein the setpoint voltage is about oneVolt.
 68. An electrochemical cell including a cathode electrode, ananode electrode, an acidic electrolyte disposed between the anodeelectrode and the cathode electrode, and a power source for applying avoltage between the anode electrode and the cathode electrode,characterized in that the anode electrode has a layer of lead dioxideelectrocatalyst facing the acidic electrolyte, a retractor mechanismbeing provided which is responsive to one or more predetermined standbyconditions to retract the anode electrode from an initial position inwhich the lead dioxide electrocatalyst is in contact with theelectrolyte to a retracted position in which the lead dioxideelectrocatalyst is spaced from the electrolyte.
 69. The cell of claim 68wherein the retractor mechanism is a passive retraction mechanism. 70.The cell of claim 68 wherein the lead dioxide electrocatalyst is β-leaddioxide, α-lead dioxide, or a combination thereof.
 71. The cell of claim68 wherein the acidic electrolyte is a proton exchange membrane.
 72. Thecell of claim 68 wherein the acidic electrolyte is an aqueous solutionof a dissolved inorganic acid, a dissolved organic acid, or a mixturethereof.
 73. The cell of claim 68 wherein the one or more standbyconditions are selected from: a voltage of less than one volt beingapplied between the first and second electrodes, the expiration of atime period of operation of the cell, an ozone concentration greaterthan a set point ozone concentration within the cell, no anodicoxygen/ozone evolution reactions occurring, and no current flowingthrough the cell.
 74. The cell of claim 71 wherein the one or morestandby conditions includes a contact pressure of less than 10 psig ofthe anode electrode with the proton exchange membrane.
 75. The cell ofclaim 68 further comprising an actuator for moving the anode electrodefrom the retracted position back to the initial position in response toone or more production conditions.
 76. The cell of claim 75 wherein theone or more production conditions are selected from: a voltage greaterthan one volt being applied between the first and second electrodes, theexpiration of a time period from termination of operation of the cell,and an ozone concentration less than a set point ozone concentrationwithin the cell.
 77. The cell of claim 71 further comprising an actuatorfor moving the anode electrode from the retracted position back to theinitial position in response to one or more production conditionsincluding a contact pressure of greater than 10 psig of the anodeelectrode with the electrolyte.
 78. The cell of claim 75 wherein theretractor mechanism and the actuator are constituted by a passive devicebiasing the anode electrode away from the electrolyte and an activemechanism which, in operation, overcomes the biasing effect of thepassive device to move the anode electrode into contact with theelectrolyte.
 79. The cell of claim 78 wherein the active mechanismreceives power from the power source so that when the power source isconnected to apply a voltage between the anode electrode and the cathodeelectrode the power source provides power to the active mechanism. 80.The cell of claim 68 wherein the lead dioxide electrocatalyst retainsits β-lead dioxide crystalline form.
 81. A method for generating ozonein an electrochemical cell having a cathode electrode, an anodeelectrode, an acidic electrolyte disposed between the anode electrodeand the cathode electrode, and a voltage source coupled between theanode electrode and cathode electrode, the method comprising the stepsof applying a voltage between the anode electrode and the cathodeelectrode characterised in that the method further comprises the stepsof initially moving the anode electrode from a retracted position inwhich it is spaced from the electrolyte to an operative position inwhich it is in contact with the electrolyte, and turning the voltagesource on before or simultaneously with the engagement of the anode withthe electrolyte, the method further comprising a step of retracting theanode electrode out of contact with the acidic electrolyte shortlybefore or simultaneously with turning off the voltage source.
 82. Themethod of claim 71 wherein the step of retracting the anode electrodeout of contact with the acidic electrolyte is effected in response tosensing of one or more predetermined standby conditions.
 83. The methodof claim 82 wherein the one or more standby conditions are selectedfrom: a voltage of less than one volt being applied between the firstand second electrodes, expiration of a time period of operation of thecell, an ozone concentration greater than a setpoint ozone concentrationwithin the cell, no anodic oxygen/ozone evolution reactions occurring,and no current flowing through the cell.
 84. The method of claim 81wherein the acidic electrolyte is a proton exchange membrane and whereinthe one or more standby conditions includes a contact pressure of lessthan 10 psig of the anode electrode with the proton exchange membrane.85. The method of any one of claims 81 wherein the engagement of theanode electrode into contact with the electrolyte is effected inresponse to the sensing of one or more production conditions.
 86. Themethod of claim 85 wherein the one or more production conditions areselected from: a voltage greater than one volt being applied between thefirst and second electrodes, the expiration of a time period fromtermination of operation of the cell, and an ozone concentration lessthan a set point ozone concentration within the cell.
 87. The cell ofclaim 80 further comprising an actuator for moving the anode electrodefrom the retracted position back to the initial position in response toone or more production conditions, wherein the acidic electrolyte is aproton exchange membrane, and wherein the one or more productionconditions includes a contact pressure of greater than 10 psig of theanode electrode with the proton exchange membrane.
 88. Anelectrochemical cell including a cathode electrode, an anode electrode,an acidic electrolyte disposed between the anode electrode and thecathode electrode, and a power source for applying a voltage between theanode electrode and the cathode electrode, characterized in that theapparatus further comprises a mechanism to retract the anode electrodeout of contact with the electrolyte in response to the absence of acurrent flowing through the electrochemical cell.
 89. An electrochemicalcell including a cathode electrode, an anode electrode, and an acidicelectrolyte disposed between the anode electrode and the cathodeelectrode, and a power source for applying a voltage between the anodeelectrode and the cathode electrode, characterized in that the apparatusfurther comprises a passive mechanism biasing the anode electrode awayfrom the electrolyte and an active mechanism which, when operative,overcomes the biasing effect of the passive mechanism to bring the anodeelectrode into contact with the electrolyte.
 90. The electrochemicalcell of claim 89 wherein the active mechanism is adapted to be actuatedwhen the power source is connected to apply the voltage between theelectrodes.
 91. An electrochemical cell including a cathode electrode,an anode electrode, an acidic electrolyte disposed between the anodeelectrode and the cathode electrode, and a power source for applying avoltage between the anode electrode and the cathode electrode,characterized in that the apparatus further comprises a mechanism toretract the anode electrode out of contact with the electrolyte tointerrupt a circuit incorporating the cell, thereby placing the cell ina standby condition.